Chapter 4 - Processing of compound semiconductors

Abstract

This chapter covers the main processing steps for groups III–V compound semiconductors, including wet and dry etching, ion implantation for doping or isolation, and ohmic and Schottky contact formation. Ohmic contact formation relative to Si is more difficult because, in general, metallic doping levels cannot be achieved in compound semiconductors and alloyed contact schemes must be relied upon. Because of the absence of reproducible oxides with low interface state densities, metal oxide semiconductor (MOS)-type devices are rare and metal semiconductor field effect transistors (MESFETs) are the most common structures. Device isolation is somewhat simpler in compound semiconductor technology because of the ability to create semi-insulating material by ion bombardment, which avoids the need for dielectric backfill or junction isolation. The presence of two or more sublattices complicates the processing of compound semiconductors because the stoichiometry must be maintained during all the individual steps. This may be difficult during thermal processes because of the high solubility of the group V elements and during dry etching because of differences in the removal rates of the different elements in the material. The chapter presents examples for each of the main III–V materials—namely, gallium arsenide (GaAs), indium phosphide (InP), and gallium nitride (GaN)—and their related ternary and quaternary alloys in addition to discussing the effect of atomic hydrogen incorporated into these materials unintentionally during growth and processing.